Login    Register
User Information
Username:
Password:
We are a free and open
community, all are welcome.
Click here to Register
Sponsored
Who is online

In total there are 56 users online :: 4 registered, 0 hidden and 52 guests


Most users ever online was 218 on Wed Dec 07, 2016 6:58 pm

Registered users: Bing [Bot], Google [Bot], MSNbot Media, Yahoo [Bot] based on users active over the past 5 minutes

The Team
Administrators
Global Moderators
global_moderators.png CS

Teflon rod piston?

Post questions and info about pneumatic (compressed gas) powered cannons here. This includes discussion about valves, pipe types, compressors, alternate gas setups, and anything else relevant.
Sponsored 
  • Author
    Message

Teflon rod piston?

Unread postAuthor: shud_b_rite » Sun Aug 05, 2007 11:12 pm

In engineering at school today I was making a bushing for a project out of teflon rod by spinning it on the lathe. Then the idea hit me, would a piece of this rod be suitable for a piston? It is easy to lathe, it is self lubricating and not that heavy.

I am currently working on my first piston valve in a 3/4 inch brass T and so far the best piston I have come up with is a battery wrapped in duct tape, but it gets munted inside the T easily, although I must admit it does work quite well.

So what do the expert piston makers think? The only problem is how to shape it since i don't have a lathe. Anyone got any tricks up their sleeve? If not I might have to try and get away with using the schools lathes.
  • 0

Airbeds... so many different uses
User avatar
shud_b_rite
1st Lieutenant
1st Lieutenant
 
Posts: 290
Joined: Tue Jan 30, 2007 7:10 pm
Location: Auckland, New Zealand
Reputation: 0

Unread postAuthor: noname » Sun Aug 05, 2007 11:14 pm

Well, Spudthug has made a couple of piston valves using teflon pistons, so I assume it would work fine.
  • 0

User avatar
noname
Lieutenant General
Lieutenant General
 
Posts: 2699
Joined: Mon Apr 10, 2006 9:19 pm
Location: Bay Area, CA
Country: United States (us)
Reputation: 9

Unread postAuthor: MrCrowley » Sun Aug 05, 2007 11:34 pm

You have engineering classes at your school? What school do you go to?
Best we have is Hard-Tech and half the credits can't be used for NCEA so its a joke of a subject really.
It should work really, if its better then a battery wrapped in duct tape there's no reason why it shouldn't work.

P.S Do you know anyone else who has made a piston valved pneumatic in NZ? So far I only know of my golfball gun and your soon to be 3/4" piston.
  • 0

User avatar
MrCrowley
Moderator
Moderator
 
Posts: 10207
Joined: Fri Jun 23, 2006 10:42 pm
Location: Auckland, New Zealand
Country: New Zealand (nz)
Reputation: 4

Unread postAuthor: shud_b_rite » Mon Aug 06, 2007 12:06 am

I am taking NCEA level 1 Engineering, thats just at the public high school in Orewa, Auckland.

I don't know of anyone else that has made a piston valve in NZ before, although... I was at an Auckland vs Bay of plenty match a while ago and i saw some people from one of the sponsors shooting foam rugby balls into the crowd. They had one person holding a tank of compressed air and another person holding the gun, I am quite sure it was a piston gun and it looked sort of home made. That and this website is the only 2 places I have ever seen a piston gun.

The one I am building is going to be used on an airsoft rifle. I have done several experiments so far and I can make a fairly large dent in a can, even more of a dent than my 300 fps airsoft piston. It will probably be done in 6 weeks or so.
  • 0

Airbeds... so many different uses
User avatar
shud_b_rite
1st Lieutenant
1st Lieutenant
 
Posts: 290
Joined: Tue Jan 30, 2007 7:10 pm
Location: Auckland, New Zealand
Reputation: 0

Unread postAuthor: MrCrowley » Mon Aug 06, 2007 12:36 am

You can make a very simple airsoft gun that is resonably compact and should be able to have a muzzle velocity of about 300m/s just with a co-axial at 150psi. I know GGDT isn't the most accurate thing out there but it gives a decent estimate.

Im also NCEA Level 1. I go to Takapuna Grammar, not sure if you have heard of it, but i've played Orewa more then a few times in Cricket, Not sure if it was your school though.
That really does suck for me, the only thing close to engineering for me is Physics, as Hard-Tech has unit or achieved standards credits, i forgot what one is the bad one but practically the whole subject is credits you can't use for NCEA.

Im going to America these upcoming holidays so I should have my airsoft gun finsihed when I get back with my suitcase full of spudgun supplies. :P

Hmm sponsors shooting a homemade piston valved gun, doesn't seem too safe, though it is NZ :D
Considering they're also illegal I doub it would be homemade, might be professionally made with a lathe and stuff so they could get a permit, I don't see NZ police permitting a homemade pneumatic gun at a rugby match.
  • 0

User avatar
MrCrowley
Moderator
Moderator
 
Posts: 10207
Joined: Fri Jun 23, 2006 10:42 pm
Location: Auckland, New Zealand
Country: New Zealand (nz)
Reputation: 4

Unread postAuthor: shud_b_rite » Mon Aug 06, 2007 12:55 am

Doesn't your school have any motor body or automotive classes? They may not have level 1 for those subjects, I know some schools start you off at level 2. Im year 12 so I'm doing level 2 for everything else but engineering.

I would also really like to build a coaxial airsoft rifle but I havent quite got my head around how they work yet. I might also make my piston gun with interchangeable barrels and chambers for firing marbles.

I just had an idea on how to shape teflon rod. Sharpen the end of a pipe like a potato cutter that many people put on the ends of their barrels, then take a size of this rod and using a vice force it into the pipe as if you were cutting a potato. Do you reckon this would work? Dam I have all these idea's and not enough time to try them all.
  • 0

Airbeds... so many different uses
User avatar
shud_b_rite
1st Lieutenant
1st Lieutenant
 
Posts: 290
Joined: Tue Jan 30, 2007 7:10 pm
Location: Auckland, New Zealand
Reputation: 0

Unread postAuthor: MrCrowley » Mon Aug 06, 2007 3:31 am

It might work if the 'potato cutter' was made out of aluminium or some strong metal I guess. Im not sure how strong teflon is.

Nah my school only has Electronics and Hard-Tech which is sh|t.
You understand how pistons work but not co-axials? A co-ax is just a piston/diaphragm gun with the barrel inside the chamber, and the piston/diaphragm seals against the barrel like a normal barrel sealer.
  • 0

User avatar
MrCrowley
Moderator
Moderator
 
Posts: 10207
Joined: Fri Jun 23, 2006 10:42 pm
Location: Auckland, New Zealand
Country: New Zealand (nz)
Reputation: 4

Sponsored

Sponsor
 


Unread postAuthor: boilingleadbath » Mon Aug 06, 2007 1:42 pm

IIRC, PTFE has a tensile strength of about 3500 psi, which puts it in the same region as UHMWPE - which, incidentally, is also low friction.

On the other hand, the melting point of UHMWPE is low enough that creep occurs (a fact which I have taken advantage of, actually) - which will tend to cause your finely machined object to change shape with time.

This isn't a major issue for our uses, though.

On a more practical note, UHMWPE is cheap... and PTFE (never mind name-brand Teflon) isn't.
PTFE is also about twice as dense.

On the topic of machining, UHMWPE cuts REALLY fast, and has to be (otherwise it melts and doesn't cut well - I suggest taking off a radius of .05" per pass in lathe work, or so). Even so, moderate-speed lathe work (I haven't tried turning it at 30 rpm or anything like that) tends to give it a terrible surface texture. And you can't sand it... just doesn't work.
Gentle heating with a propane torch can melt the surface of the UHMWPE, which cools to a really smooth (heck, reflective) finish - although I don't know how this effects the dimensions of the piece.

I don't know anything about machining PTFE.

Cutting either plastic with a steel spudcutter or similar will require a lot of force, as you have to expand the waste material over the cutter as you cut... and, besides, making a steel spudcutter basically requires a lathe anyways.
With a vice, I'd expect you to get a curved piston.
  • 0

User avatar
boilingleadbath
Moderator
Moderator
 
Posts: 1642
Joined: Sat Mar 12, 2005 10:35 pm
Location: Pennsylvania, USA
Reputation: 0

Unread postAuthor: pyromanic13 » Mon Aug 06, 2007 2:37 pm

they use it for paintball guns, sounds great for your purposes.
  • 0

Movie dialogue: "The good die first."
Tom: "But most of us are morally ambiguous, which explains our random dying
patterns."

pyromanic13
Brigadier General
Brigadier General
 
Posts: 913
Joined: Wed Oct 19, 2005 7:54 pm
Reputation: 0

Unread postAuthor: Scotty » Mon Aug 06, 2007 9:51 pm

PTFE Machines like butter, it's not real rigid though.
Nice to know there are fellow machinists on the forum :P

Peace
Scotty
  • 0


Scotty
Staff Sergeant
Staff Sergeant
 
Posts: 114
Joined: Tue Jan 09, 2007 3:00 am
Reputation: 0

Unread postAuthor: shud_b_rite » Mon Aug 06, 2007 11:46 pm

I know, its fun turning PTFE because it is so easy to cut. I got a couple of scrape pieces from school and took my aluminum pipe and sharpened it on a grinder and then stuck it in the vice with some PTFE, it worked for about 7mm but past that it just started warping the pipe in weird shapes as the PTFE got pushed inside it.

UHMWPE is another good idea. I'm gonna try and get on the lathe tomorrow at school, I should easily be able to get it done. If not I'll take it to my local engineering workshop and ask them to do it for me.
  • 0

Airbeds... so many different uses
User avatar
shud_b_rite
1st Lieutenant
1st Lieutenant
 
Posts: 290
Joined: Tue Jan 30, 2007 7:10 pm
Location: Auckland, New Zealand
Reputation: 0

Unread postAuthor: Scotty » Tue Aug 07, 2007 1:03 am

Offer to pay them in beer- It will be a lot cheaper 8)
1 piston = 1 beer!

Peace
Scotty

P.s. Check out www.gloryetp.com.au (Our Workshop)
  • 0


Scotty
Staff Sergeant
Staff Sergeant
 
Posts: 114
Joined: Tue Jan 09, 2007 3:00 am
Reputation: 0

Unread postAuthor: shud_b_rite » Wed Aug 08, 2007 4:51 am

Do you think it would be wise for me to melt PTFE using propane torch and pour it into a mould? Im not sure if it would give off poisonous fumes because it is simply made up of chains of CF2, I cant find anything on the net about it either.

I know PTFE melts at 280 Celsius which is easily reachable with a propane torch. I am also worried about over heating it which could cause it to bubble and spit like when you put water and oil on the BBQ.

I might set up a little experiment tomorrow to see if it will work.
  • 0

Airbeds... so many different uses
User avatar
shud_b_rite
1st Lieutenant
1st Lieutenant
 
Posts: 290
Joined: Tue Jan 30, 2007 7:10 pm
Location: Auckland, New Zealand
Reputation: 0

Unread postAuthor: frankrede » Wed Aug 08, 2007 2:23 pm

I read that burning teflon creates a extremely deadly gas
  • 0

Current project: Afghanistan deployment
User avatar
frankrede
Lieutenant General
Lieutenant General
 
Posts: 3220
Joined: Thu Jul 20, 2006 9:47 pm
Reputation: 0

Unread postAuthor: noname » Wed Aug 08, 2007 2:33 pm

Really?
<a href="http://www.spudfiles.com/forums/files/leakymeter_010_159.jpg">oopsies...</a>
  • 0

User avatar
noname
Lieutenant General
Lieutenant General
 
Posts: 2699
Joined: Mon Apr 10, 2006 9:19 pm
Location: Bay Area, CA
Country: United States (us)
Reputation: 9

Next

Return to Pneumatic Cannon Discussion

Who is online

Registered users: Bing [Bot], Google [Bot], MSNbot Media, Yahoo [Bot]

Reputation System ©'